To implement asynchronous receiving and sending of signals on a plurality of frequency bands, generally, each frequency band corresponds to a radio frequency front-end. If a same radio frequency front-end is used to perform asynchronous receiving and sending on different frequency bands, a saturated analog-to-digital converter (ADC) of a receiving channel is caused. For example, maximum power of a transmit signal is 30 dBm, and power of a received signal is −90 dBm to −50 dBm. Although a self-interference signal and the received signal are on different frequency bands, the ADC includes signals that are on all frequency bands to perform sampling. Therefore, the received signal is submerged in noise because of the self-interference signal.
FIG. 1 is an architectural diagram of a signal processing system in the prior art. As shown in FIG. 1, a duplexer is used at a radio frequency front-end to separate a transmit signal from a received signal, so as to weaken, as much as possible, a self-interference signal that the transmit signal leaks, in an out-of-band way, to a frequency band of the received signal.
However, a technology for separating a transmit signal and a received signal based on a duplexer has the following problems: For example, a cavity duplexer used by a base station has characteristics of a large volume and a high cost, which increases difficulty and a cost of system layout; for another example, a dielectric duplexer used by a mobile terminal has a characteristic of high energy consumption, which significantly deteriorates receiving quality for receiving a downlink signal.